If your corporation owed more than $3,000 in tax last year, the CRA likely expects you to pay this year’s tax in instalments rather than in one balance at year-end. Miss those instalments, or underpay them, and the CRA charges interest that compounds daily. Most owners do not find out until the bill arrives with their assessment.
This is one of the most common and most avoidable sources of CRA interest for Canadian small businesses. Here is how instalments actually work in 2026, and how to stay ahead of them.
Who has to pay instalments
The rule is straightforward. If your total tax payable is more than $3,000 in either the current year or a prior year, the CRA generally requires instalment payments. New corporations are usually exempt in their first year, because there is no prior-year tax to base instalments on.
The $3,000 figure refers to federal and provincial tax combined, not each separately. For a business in British Columbia, that threshold comes up faster than owners expect, because BC corporate tax is calculated on the same T2 and administered by the CRA alongside the federal amount.
There is a common point of confusion worth clearing up. Instalments are not an extra tax. They are pre-payments toward the tax you will owe anyway, spread across the year so the CRA collects as you earn rather than in one lump at the end. The only thing instalments cost you, if you handle them correctly, is the discipline of paying on schedule. The interest only appears when you pay late or pay short. Owners who treat instalments as a budgeting rhythm rather than a surprise rarely pay a dollar of instalment interest.
Monthly or quarterly
All corporations are allowed to pay monthly. Some Canadian-controlled private corporations qualify to pay quarterly instead, which is easier on cash flow because the payments are spread across four dates rather than twelve.
Quarterly eligibility is not automatic. It depends on having a clean compliance history. The CRA looks at whether, over the prior twelve months, you remitted GST/HST, payroll source deductions, CPP, and EI on time, and filed all required returns on time. Slip on any of those and you can lose quarterly eligibility and revert to monthly. The lesson is that staying compliant everywhere protects your flexibility on instalments.
The three ways to calculate what you owe
The CRA gives you three options for calculating instalments, and you are allowed to use whichever produces the lowest payments.
Option one bases payments on your estimated tax for the current year. Option two bases them on last year’s actual tax. Option three uses a blend of the two prior years. Option two and option three are the safe choices, because they are based on amounts that are already known. If you use them and pay on schedule, the CRA will not charge instalment interest even if your actual tax for the year ends up higher.
Option one is the trap. If you estimate the current year low to reduce your payments, and your actual tax comes in higher, the CRA charges interest on the shortfall. Use option one only when you are confident this year’s income is genuinely lower than last year’s.
How the interest actually works
Instalment interest is charged when payments are late or short. It compounds daily at the CRA’s prescribed rate, which means a missed instalment early in the year quietly grows for months before you ever see the bill.
There is a mechanism that works in your favour here. If you have fallen behind on instalments, you can reduce or eliminate the interest by overpaying a later instalment or paying it early. The CRA effectively nets the timing out. So if you realize in September that you underpaid in the spring, you are not stuck. You can catch up and limit the damage.
The mid-year review that prevents the surprise
Instalments set in January are based on an estimate. By July, you have six months of actual results, and you usually know whether the year is tracking ahead of or behind your original estimate.
This is the moment to check. If the year is running stronger than last year and you set instalments on the low side, increasing your remaining payments now avoids a large balance and interest at year-end. If the year is running softer, you may be overpaying and tying up cash you could use elsewhere. Either way, the only way to know is to compare your instalments to your projected liability against actual results, and the only way to do that reliably is to have books that are current.
That is the practical link between bookkeeping and tax. You cannot make a good instalment decision in July if your books stop at March.
What to do now
Confirm whether you are required to pay instalments, and on what schedule. Check which calculation option you are using and whether it still makes sense given how the year is going. And if your books are not current enough to project your liability, fix that first, because every instalment decision depends on it.
This is exactly the kind of forward-looking review we build into monthly advisory work. If you want a clear read on your instalment position before year-end, book a free Diagnostic and we will walk through where you stand.
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